624
Journal of the American Chemical Society
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102.2
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January 16, 1980
An NMR Spectroscopic and X-ray Crystallographic Study of the Reaction of Tris( dimethy1amino)chlorosilane with Aluminum Chloride. A Quest for the Elusive Silicenium Cation A. H. Cowley,* M. C. Cushner, and P. E. Riley Contribution f r o m the Department of Chemistry, The Uniaersity of Texas at Austin, Austin, Texas 78712. Receiued July 2, 1979
Abstract: The reaction of (Me2N)jSiCI with Alp& in CH2Cl2 has been carried out over a range of stoichiometries in an effort to prepare the [(Me2N)3SiIt ion. In the solid phase the product forms as colorless crystals of (Me2N)3SiCI.AIC13 in orthorhombic space group Pbca, with unit cell constants at -35 " C a = 14.718 (14) A, b = 12.379 (7) A, and c = 33.442 (21) A. The calculated density of 1.441 g is reasonable for 16 molecules of ( M ~ ~ T v ) ~ S ~ C I . Aper I Cunit I ~ cell. Full-matrix leastsquares refinement of the structure, using the 3646 symmetry-independent reflections for 4 < 28 < 48" which have I , > 2.Ou(I0), has converged with a conventional R index (on IFI) of 0.060. The bonding in each (Me2N)3SiCLAICI3 is such that one of the Me2N groups is involved in a donor-acceptor bond with an AICl3 unit. In solution the reaction has been investigated by 'H, I3C,27Al, and 29SiN M R spectroscopy. A preliminary study of the interaction of (Me2N)3SiF with the fluoride ion acceptors PF5 and AsF5 revealed that these reactions are apparently complex and do not result in significant fluoride ion abstraction.
Introduction The literature records numerous unsuccessful attempts to isolate tricoordinate silicon (silicenium) cations.' Despite this body of negative results, it is interesting to note that silicenium cations are readily observable in the vapor phase by mass spectrometry2 and ion cyclotron resonance (ICR)3 techniques. Indeed, it has been found both experimentally3 and theoretically4 that in the gas phase the parent silicenium ion, SiH3+, is more stable than the analogous carbocation. Since amino groups are widely recognized to function as effective K donor^,^ we decided to attempt stabilization of the tricoordinate Si+ center with MezN ligands. Since halide ion abstraction has proved to be an effective means of synthesizing two-coordinate phosphorus cations,6 one obvious approach to the corresponding silicon chemistry was to treat tris(dialky1amino)silyl halides with halide ion acceptors. The present paper describes the reactions of (Me2N)3SiX (X = CI, F) with Al2Cl6, PF5, and AsF5. Reactions in solution were investigated by N M R spectroscopy. A single-crystal X-ray diffraction study has been performed on the solid resulting from the reaction of (Me2N)3SiC1 with Al2C16. Experimental Section General Procedures. Virtually all the materials described herein are moisture sensitive. Accordingly, volatile compounds were manipulated in a high-vacuum system of conventional design and less volatile materials were handled in an inert atmosphere. Spectroscopic Measurements. The ' H and I9F N M R spectra were recorded on A-60 and A-56/60 spectrometers, respectively. The ' H and I9F chemical shifts were measured relative to internal CH2C12 (6 5.34 ppm relative to Me4Si) and external CC13F, respectively. The 13CN M R spectra were measured on a Bruker WH-90 spectrometer operating at 22.6 MHz and referenced to interpal CH2C12 (6 54.2 ppm relative to Me&). The 27AIspectra were recorded on a Varian HA100 spectrometer operating at 26.05 MHz and featuring a locally built cross-correlation system and external deuterium lock. Hydrated A13+ and [Me4N]+[AIC14]- were employed as primary and secondary external references, respectively. The IySi N M R experiments were performed on a Varian XL-100 spectrometer at the University of H o ~ s t o n This . ~ instrument was operated in the Fourier transform mode and featured a tunable probe. The 29Sichemical shifts are referenced to external Me& For all the above nuclei a positive chemical shift implies that the resonance occurs at higher frequency than that of the primary reference. 0002-7863/80/ 1502-0624$01 .OO/O
Infrared spectra were obtained using a Perkin-Elmer Model 337 grating spectrophotometer. Materials. Tris(dimethylamino)chlorosilane, Al2C16, n-BuLi, Me2NH, SiF4, PF5, and AsF5 were procured commercially. All volatile materials were purified by trap-to-trap distillation in vacuo prior to use. The aluminum chloride was sublimed at least twice in evacuated sealed tubes using a Scientific Instrument Accessories Model 240 thermal gradient sublimer. Reagent grade CH2Cl2 was distilled from CaH2 at reduced pressure and stored over CaH2'in the dark. Anhydrous diethyl ether was used without further purification. Preparation of Tris(dimethy1amino)fluorosilane. The procedure employed is similar to the one described by Wannagat et a1.8 for the synthesis of (EtzN)$iF. Dimethylamine (55.5 mmol) and ca. 60 mL of dry Et20 were condensed in vacuo at -196 "C into a 250-mL round-bottomed flask equipped with a magnetic stirring bar. The reaction vessel was removed from the vacuum line and charged with 55.5 mmol of n-BuLi (n-hexane solution) while the contents were maintained at -196 "C. The reaction mixture was then allowed to warm to ambient temperature, stirring being maintained for 1.O h. Following this, the reactor was connected to the vacuum system, cooled to -22 "C, and exposed to 46.25 mmol of SiF4. When the pressure in the system reached equilibrium, all volatiles were condensed into the reaction vessel. The flask was then allowed to warm to ambient temperature and was heated subsequently for ca. 5 min at 60 "C before fractionating the volatiles with U-traps held at -22, -50, and -196 'C. Clear, colorless liquid (Me2N)3SiF (1.52 g, 8.5 mmol) was isolated, representing a yield of 46.0%. NMR: IH, doublet, 6 2.46 ppm, J F ~ ~ N = 1.3 CH Hz; I9F, broad singlet, 6 152.4 ppm. IR: u(SiF) 862 cm-l; u(SiN) 739 cm-l. Reaction of (Me21V)fiiCI with A12C16. In a typical experiment 0.464 g (2.37 mmol) of (Me2N)3SiCI was condensed in vacuo onto 0.3 16 g (1.185 mmol) of AI2C16 contained in a IO-mL round-bottomed flask at - 196 "C. After condensation of ca. 2 mL of CH2C12, the reaction mixture was agitated frequently and allowed to assume ambient temperature. This treatment resulted in a colorless solution. NMR: ' H , singlet, 6 2.74 ppm; I3C, singlet, 6 40.4 ppm; *'AI, broad singlet, 6 $107 ppm; 29Si(-60 "C), singlet, 6 -25.3 ppm. Reaction of (MezN)$iF with MF5 (M = P, As). In a typical experiment 0.095 mmol of (MezN)$iF, 0.05 mL of C6HsCF3, and ca. 0.2 mL of CH2C12 were condensed at -1 96 "C intoa 5-mm0.d. NMR tube connected to a vacuum system by means of a stopcock and standard taper joint. The mixture was thawed, mixed thoroughly by agitation, and recooled to - 196 "C prior to the addition of 0.095 mmol of MFs ( M = P, As). Following this, the N M R tube was sealed and allowed to warm to ambient temperature while the contents were mixed by vigorous shaking. ' H and I9F N M R spectroscopic assays revealed (a) the presence of at least ten ' H or I9F resonances and (b) the virtual absence of PF.5- or AsF6-.
0 1980 American Chemical Society
Cowley, Cushner, Riley
/ Reaction of (MelN)3SiCl with AIlC16
Crystallographic Section. Single crystals of the solid obtained from the reaction of (Me2N)$iCI with AlzC16 were grown by allowing a supersaturated CH2C12 solution to stand for several hours at -30 'C. A satisfactory specimen cut from a large, colorless tablet was glued to a glass fiber which was affixed to a brass pin and joined to a goniometer head. The crystal was then quickly transferred to a Syntex P21 automated diffractometer where it was maintained in a stream of cold (-35 'C), dry nitrogen during the course of all subsequent crystallographic experiments. Preliminary examination of the crystal with the diffractometer indicated orthorhombic symmetry consistent with space group Pbca (no. 61). Crystal data and data collection details are summarized in Table I. The measured X-ray diffraction intensities were reduced and assigned standard deviations (with p = 0.03) as described p r e v i o ~ s l y . ~ Although the density of these crystals was not determined experimentally because of the aforementioned air/moisture sensitivity, the calculated value of 1.441 g cm-' assuming 16 formula weights per unit cell of [(MezN)3Si]AIC14 is plausible. Since solution of the crystal structure requires the location of two (crystallographically independent) formula weights of [(Me2N)&]AIC14 per asymmetric unit in space group Pbca, it was deemed expedient to initiate structure solution by direct methods ( M U L T A N ) . ~Satisfactory ~ solution of the structure was ultimately obtained by the application of direct and heavy-atom meth0ds.l I However, as confirmed by successful fullmatrix least-squares refinement of the structure (discussed below), (Meh
625
Table 1. CrvstallograDhic Summarv Crystal Data at -35 "C" 14.718 (14) 12.379 (7) 33.442 (21) c, A v,A3 6093 (13) dcalcd, g ~ 1 1 7 ~ ~ 1.44lb empirical formula CsH i8AIC14NjSi crystal system orthorhombic Okl. k = 2n t 1 systematic absences h01, I = 212 1 hkO, h = 217 t 1 Pbca (no. 61) space group 16 Z F(000).electrons 2720 329.14 formula wt a, A b, 8,
+
Data Collection at -35 'CC 0.710 69 radiation (Mo Ka)..A mode w scan symmetrically over 1 .O' about scan range Kal,2 maximum offset 1.O and - I .Oo in w from background K a l , maximum ~ variable, 3.0-6.0 scan rate, deg min-l 4 remeasured after every 96 check reflections reflections; analysiscfof these data indicated a continuous decline in intensity to a maximum of ca. 8% at the conclusion of data collection (64 h of X-ray exposure). [or which the appropriate correction was applied 20 range, deg 4.0-48.0 total reflections measd 4775 0.40 X 0.74 X 0.82 data crystal dimensions, mm 8.84p absorption coeff, d M o Ka).cm-l
1 the crystal structure consists not of the desired [(MezN)3Si]+ and AIC14- ions but rather of the Lewis acid-base adduct 1. (Consistent with the calculated density, there are two molecules of 1 per asymmetric unit.) The function minimized in least-squares refinement is C w ( IFo/ IFcI)2,where the weight w is ~ ( l F ~ l )the - ~reciprocal , square of the standard deviation of each observation, I FoI, Neutral atom scattering factors for CI, Si, AI, N, and C12 were used in these calculations, and the real (Af) and imaginary (AS') correctionsI2 for anomalous Unit cell parameters were obtained by least-squares refinement scattering were applied to the C1, Si, and AI scattering curves. of 30 reflections with 22.0 < 28 < 23.9'. Owing to air/moisture Least-squares convergence was attained using only those 3646 data sensitivity an experimental density was not obtained. Sqntex P2i with I o / u ( I o )> 2.0 for a structure in which all nonhydrogen atoms autodiffractometer equipped with a graphite monochromator and a were ultimately refined anisotropically, with R = lFol - IFc[ I / Syntex LT- 1 inert-gas low-temperature delivery system. Henslee, CIFol = 0.060, R, = [ x w ( l F 0 l - I F c ~ ) 2 / ~ ~ ~ ~ 0=10.081, 2 ] 1 / 2 W. H.; Davis, R. E. Acta Crystallogr., Sect. B 1975.31, I5 1 l . Since IFo[ and a standard deviation of an observation of unit weight = the data crystal was cut from a larger specimen and since the crystal - IFcl)2/(m- s ) l i i 2 = 3.38, for m = 3646 observations and s = 271 faces were severely eroded at the conclusion of data collection as a variables. No attempt was made to locate the hydrogen atoms. Despite consequence of the decay mentioned above. an absorption correction omission of the contributions of the hydrogen atoms to the calculated based upon the diffractometer setting angles of the crystal faces was structure factors, examination of the data near the conclusion of renot applied to the data. The range in transmission factors based upon finement indicated that several low-angle reflections were possibly the extreme dimensions of the crystal is 0.48--0.70. affected by secondary extinction. However, since the incorporation of Zachariasen's coefficienti3for this effect produced no significant of those involving the unlocated hydrogen atoms; see Experichanges in the structural parameters or the values of the calculated mental Section) are greater than the accepted van der Waals structure factor amplitudes and since it refined to a value not significantly different from zero, it was not included in the final cycles of contact distances. There is no apparent pseudosymmetry which refinement. A structure-factor calculation using the atomic paramapproximately relates the atoms of the two molecules (A and eters obtained a t least-squares convergence with all 4775 reflections B) of the asymmetric unit. Figure 1 provides a stereoscopic measured during data collection gave R and R, values of 0.089 and view of molecule A and indicates the atom numbering scheme 0.082, respectively. used for both molecule A and molecule B. As shown by comIn the final cycle of refinement no shift in an atomic parameter parison of the bond lengths and bond angles in Table 111, the exceeded 25% of a corresponding estimated standard deviation (esd). molecular geometries of the two independent molecules arc The largest peaks on a final difference Fourier map were 0.3-0.6 e A-3 in excellent agreement. Furthermore, these values for and were associated with the methyl carbon atoms (and presumably (Me2N)3SiCLAIC13agree with values obtained for numerous their omitted hydrogen atoms). Table I1 presents atomic positional and thermal parameters, with other structural determinations of similar molecules. The only corresponding esd's as estimated from the least-squares inverse matrix. significant difference in the structures of molecules A and B A tabulation of observed and calculated structure factor amplitudes Cl C1 is a ~ a i 1 a b l e . l ~
-
[xw(
Results and Discussion The crystal structure consists of discrete molecules of (Me2N)3SiCI.AIC13, each formed by the coordination of an AlC13 moiety to one of the nitrogen atoms of a (Me2N)3SiCI molecule. All nonbonded intermolecular distances (exclusive
molecule A
molecule B
Journal of the American Chemical Society
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1 102:2 1 January 16, 1980
Table 11. Fractional Coordinates and Anisotropic Thermal Parameters ( X IO3) for Atoms of (Me2N)3SiCI-AICI3" atom CI(A1) Cl(A2) CI(A3) CI(A4)
X
Y
0.8639(1) 0.9065 ( I ) 1.0226 ( I ) 0.7961 ( I ) 0.9229 ( I ) 0.8990 ( I ) 0.8582 (3) 0.9143 (4) 1.0314 ( 4 ) 0.75.50 (4) 0.8727 ( 5 ) 0.83 I7 ( 5 ) 0.9832 (6) 1.0768 ( 5 ) 1.0975 ( 5 ) 0.491 I ( I ) 0.3876 ( I ) 0.1959 ( I ) 0.2836 ( I ) 0.4479 ( 1 ) 0.3164 ( I ) 0.3965 (3) 0.5357 (4) 0.3702 (4) 0.33 I4 ( 5 ) 0.4676 ( 5 ) 0.5939 ( 5 ) 0.5828 (6) 0.3043 ( 5 ) 0.3592 (5)
0.6348 (2) 0.4437 ( I ) 0.6055 (2) 0.5460 (2) 0.7347 ( I ) 0.5770 (2) 0.7086 (4) 0.8656 (4) 0.6979 (4) 0.6967 (6) 0.7997 ( 5 ) 0.93 I4 (6) 0.91 25 (6) 0.6026 (6) 0.7744 (7) 0.9606 ( I ) 0.5107 ( I ) 0.6776 (2) 0.6087 (2) 0.8039 ( 1 ) 0.6415 (2) 0.7690 (4) 0.7247 (4) 0.8043 (4) 0.8612 ( 5 ) 0.7580 (6) 0.6543 (6) 0.7589 (7) 0.8909 (6) 0.7140 (6)
u1 I 0.8742 ( 1 ) 0.7973 ( I ) 0.7276 ( 1 ) 0.7146 ( I ) 0.8328 (0) 0.7579 ( 1 ) 0.7870 ( I ) 0.8458 (2) 0.8265 (2) 0.7948 (2) 0.7568 (2) 0.8452 (2) 0.8728 (2) 0.8427 (2) 0.8069 (2) 0.9429 ( 1 ) 0.9558 ( I ) 0.9498 ( I ) 1.0418 ( I ) 0.9340 ( 1 ) 0.9814 ( I ) 0.9823 ( 1 ) 0.9216 (2) 0.8971 (2) 0.9950 (2) 1.0151 (2) 0.9464 (2) 0.8836 (2) 0.8888 (2) 0.8691 (2)
u22
u33
54(1) 34(1) 73(1) 57(1) 32(l) 33(1) 29(3) 35 (3) 45 (3) 52 (4) 33 (4) 43 ( 4 ) 54(5) 54(5) 70(5) 30(1) 32(1) 56(1) 57(1) 25 ( I ) 29(1) 27 (3) 40(3) 36(3) 29(4) 59 ( 5 ) 51 ( 5 ) 83 (6) 37 (4) 59(5)
39(1) 59(1) 60(l) 61 ( I ) 31 ( I ) 39(1) 37 (3) 50(3) 41 (3) 74(5) 49 ( 4 ) 63 ( 5 ) 70(5) 67 (5) 79(6) 60(1) 67(1) 70(1)
U12
u13
u23
SO(1)
35(1) 40(1) 34(3) SO(3) 38 (3) 59(5) 36 (3) 73 ( 5 ) 59(5) 67 ( 5 ) 41 (4)
a See Figure I for identity of the atoms. Numbers in parentheses throughout the table are the estimated standard deviations in the units of the least significant digits for the corresponding parameter. The U , are the mean-square amplitudes of vibration in A2 from the general temperature factor expression exp[-27r2(U~ ~ h ~ +a * ~ U3312c*2 2Ul2hka*b* + 2U13hla*c* + 2U23klb*c*)].
+
+
c L4
c1
Figure 1. Stereoscopic view of molecule A of (MezN)3SiCI.AIC13, illustrating the atom-numbering scheme used for both independent molecules of the structure. Atoms are shown as ellipsoids of 30% probability. As stated in the text, the hydrogen atoms were not located in this study.
is conformational, as shown below, which is consistent with the presumed low barrier of rotation about the Si-N(sp3) single bond. The structure of the donor fragment (MezN)3SiCI has been determined by gas-phase electron diffraction methods. When nitrogen atom N ( 1) undergoes coordination with an AIC13 unit, three major structural modifications ensue (see Table IV): (1) the coordination geometry of N( 1) changes from trigonal planar to tetrahedral, (2) the Si-N( 1 ) bond lengthens by 0.12-0.16 A, and (3) the C-N(1) bonds increase by ca. 0.07 A. The major point of interest in the structure of (Me2N)3SiCIsAIC13 concerns the fact that both tetrahedral and trigonal planar nitrogen atoms are bonded to the same silicon atom. Thus, N( 1) is virtually tetrahedral (average bond angle 109.4'
in both molecules A and B), while the average sums (for molecules A and B) of bond angles are 356.4 and 359.8O for N(2) and N(3), respectively. Furthermore, the average N ( 1)-Si bond length (1.836 A) is significantly lar er than the average N(2)-Si or N(3)-Si bond length (1.679 ). The sensitivity of N-X bond lengths to the geometry at the nitrogen center is now well documented for compounds with, e.g., N-PI6 and N-SiI7 bonds. Typically, for a tetrahedrally coordinated nitrogen atom the N-X bond lengths approach the sum of the covalent radii (1.87 AI8 in the case of the N-Si bond), whereas for a trigonal planar nitrogen atom this bond is shortened appreciably. These observations can be rationalized by postulating a px-dx component to the N-X bond when the nitrogen atom is trigonal ~ 1 a n a r . However, l~ it is sometimes possible to discuss the
x
Cowley, Cushner, Riley Table 111. Bond Lengths
Si-CI( I ) Si-N(I) Si-N(2) Si-N(3) N ( 1 )-C( 1) N(I)-C(2) N(2)-C(3) ~(2)-~(4) N(3)-C(5) N(3)-C(6) AI-N(I) AI-Cl(2) AI-CI( 3) AI-Cl(4) CI( I)-Si-N( I ) CI( I)-Si-N(2) CI( I)-Si-N(3) N ( I)-Si-N(2) N ( 1 )-Si-N( 3) N(2)-Si-N( 3) Si-N( I)-AI Si-N( I)-C( 1) Si-N ( 1 ) -C( 2) AI-N( l ) - C ( l ) AILS( I)-C(2) C ( I )-N( 1 )-C( 2) Si-N(2)-C(3) Si-N (2)-C( 4) C(3)-N(2)-C(4) Si-N(3)-C(5) Si-N(3)-C(6) C ( 5) -N (3) -C( 6) N ( I)-Al-C1(2) N ( I)-Al-C1(3) N ( 1 ) - AI-CI( 4) C1(2)-AI-C1(3) C1(2)-AI-C1(4) CI( 3)-AI-C1(4)
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621
Reaction of (Me2N)3SiC1 with Al2Cl6
(A) and Bond Angles (deg)" molecule A
molecule B
2.050 (2) 1.832 (5) 1.684 (6) 1.674 (5) 1.549 (8) 1.528 (8) 1.465 (9) 1.478 (10) 1.460 (9) 1.510 (9) 1.990 ( 5 ) 2.115 (3) 2.111 (3) 2.130 (3)
2.062 (2) 1.835 (5) 1.674 (6) 1.683 (5) 1.550 (8) 1.522 (8) 1.478 (9) 1.510 (10) 1.472 (9) 1.468 (9) 1.972 (5) 2.111 (3) 2.1 12 (3) 2.1 18 (3)
103.8 (2)
102.8 (2) 110.4 (2) 108.2 (2) 1 13.5 (3) 111.4(2) 110.2 (3) 1 15.0 (3) 108.9 (4) 1 1 1.8 (4) 102.9 (4) 110.5 (4) 107.0 (5) 130.9 (5) 113.5 ( 5 ) 1 11.8 (5) 126.1 (4) 122.7 (4) 111.2(5) 108.8 (2) 109.9 (2) 106.0 (2) 112.1 ( I ) 110.7 ( I ) 109.1 ( I )
1 12.0 (2)
109.0 (2) 110.3 (3) 110.1 (2) 1 11.5 (3) 113.3 (3) 1 12.7 (4) 110.5 (4) 107.5 (4) 103.9 (4) 108.5 ( 5 ) 126.4 ( 5 ) 1 19.0 ( 5 ) 1 1 1.1 (5) 127.7 (5) 119.9 (5) 111.9(5) 110.5 (2) 11 1.0(2) 105.4 (2) 112.6 ( I ) 108.6 ( I ) 108.5 ( I )
a Numbers in parentheses are the estimated standard deviations in the least significant digits. See Figure 1 for identity of the atoms.
structural trends in such molecules in terms of other orbital interactions. 2o The increase of N-C bond lengths upon coordination of the nitrogen atom has been observed previously. In fact, using Me3N as a reference base it has been suggested21 that the increase of the N-C distances is an indication of the stability of the X3AI complex. The N AI and AI-CI bond lengths in (Me2N)3SiCI.A1C13 are very similar to those in other monoamine complexes such as Me3N.A1C13.21 The identity of the solution species resulting from the reaction of (Me2N)3SiC1 with A12C16has not been established
-
I
' Y W d LAqqJd Figure 2. (a) I3C N MR spectrum of (Me2N)3SiCLAICI3with a 33% excess of (MezN),SiCI in CH2C12 solution at -90 "C. (b) *'AI NMR spectra of AI&- (sharp resonance) and (Me2N)3SiCI.AIC13 (broad resonance).
as well as that of the solid-state material. At ambient temperature the 'H and I3C N M R spectra of 1:l mixtures of (Me2N)3SiC1 and AlC13 units consist of singlets shifted downfield by 0.24 and 3.1 ppm, respectively, from those of unreacted (Me2N)$iCI. In the presence of excess (Me2N)3SiC1 two resonances are clearly apparent in both the 'H and I3C spectra, thus indicating that, on the N M R time scale, the exchange between free and coordinated (Me2N)3SiCI is not significant. Examination of the integrated areas of free and complexed (Me2N)3SiCI indicates a composition of 1:1 stoichiometry, viz., (Me2N)3SiCI.AlC13. The I3C spectrum of (Me2N)$iCI in solution with a 30% excess of AIC13 units exhibits a sharp singlet shifted downfield by only 0.5 ppm from that of (Me2N)3SiCl-AlCl3. This small shift could indicate the presence of a small amount of a bis adduct, (Me2N)3SiCL2AlCI3, in dynamic equilibrium with the mono adduct. However, it is probably due to the presence of Al2C16 in the solution. Figure 2a illustrates the observation that sig-
Table IV. Comuarison of Structural Data for (Me7N)qSiCI and (Me7N)&iCI.AICIP
Si-N, A C-N, Ad
SN,deg
1.715 (2) 1.462 (5) 359.5
deviations of N from its Si, C, C plane, 8, 6.den
22.5
1.832 (5) 1.538 (10) 0.512 (5) 38
1.684 (6) 1.472 (6) 356 (2) 0.164 (5) 15
1.674 (5) 1.485 (25) 360 (2) 0.063 (5) 15
1.835 ( 5 ) 1.536 (14) 0.547 (5) 8
1.674 (6) 1.494 (16) 356 (2) 0.173 (5) 20
1.683 (5) 1.470 (2) 360 (1) 0.008 (5) 33
Numbers in parentheses are the estimated standard deviations in the least significant digits. SNcorresponds to the sum of the angles about the nitrogen atoms. 6 represents the angle of twist from the conformation in which the Si, C1, N(i) (i = I , 2, or 3) plane is perpendicular to the C, N(i), C plane. Reference 15. See Figure 1 for identity of the atoms. Mean C-N bond lengths are listed. Omission of the hydrogen atoms in structure refinement tends to lengthen artificially the determined C-N distances (see text).
628
Journal of the Americari Chemical Society
nificant exchange broadening does not occur in the I3C resonance of a typical mixture containing excess (Me2N)jSiCI even a t -90 O C . Thus, if the structure of (Me2N)3SiCLAIC13 in solution is the same as that in the solid state, the AICI3 moiety must be averaging among all three nitrogen sites fairly rapidly. The foregoing conclusions are consistent with the 27AlN M R data for a 1 :1 mixture of (Me*N)3SiCl and AIC13 units (Figure 2b), since the l7AI chemical shift of (Me2N)3SiCI.A1C13 (+lo7 ppm) is close to that of other R3E-AIC13 complexes, such as M e 3 P ~ A l C 1 3The . ~ ~ 29SiN M R data were difficult to obtain, possibly owing to quadrupolar relaxation effects associated with the I4N nuclei. However, on cooling the samples (equimolar i n (Me*N)$iCI and AIC13 units) to -60 "C it was possible to detect singlet resonances. The chemical-shift difference between (Me*N)3SiCI and that which we attribute to (Me2N)$iCI*AIC13 is surprisingly small. The interaction of (MeZN)3SiF with the fluoride ion acceptors PFs and ASFSwas explored as a potential synthetic route to the [(MezN)$i]+ ion. These reactions are apparently complex, resulting in the appearance of several new resonances. However, none of these resonances was attributable to PF6or AsF6-; hence, this line of experimentation was not pursued further. Current efforts to synthesize silicenium ions involve the use of cyclic precursor halides and silyl halides with both bulky and a-donor substituents. Acknowledgment. The authors are grateful to the National Science Foundation (Grant CHE76-10331) and the Robert A. Welch Foundation for generous financial support. We also wish to thank the National Science Foundation for the purchase of the Syntex P21 diffractometer, and Professor Raymond E. Davis for his interest and assistance in this work. Supplementary Material Available: A tabulation of observed and calculated structure factor amplitudes (22 pages). Ordering information is given on any current masthead page.
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References and Notes (1) For recent reviews, see: (a) Corriu. R. J. P.; Henner, M. J. Orpnomet. Cbem. 1974, 74, 1. (b) O'Brien, D. H.; Hairston, T. J. Orpmmet. Chem. Rev., Sect. A. 1971, 7, 95. For more recent papers on this subject, see, for example, (c) Lambert, J. B.; Sun, H. J. Am. Chem. SOC.1976, 98, 56 11. (d) Barton, T. J.; Hovland, A. K.; Tully. C. R. lbid. 1976, 98, 5695. (e) Olah, G. A,; Mo, Y. K. /bid. 1971, 93, 4942. (2) (a) Weber, W. P.; Felix, R. A,; Willard, A. K. TetrahedronLett. 1970. 907. (b) Litzow, M. R.; Spaulding, T. R. "Mass Spectrometry of Inorganic and Organometallic Compounds", Physical Inorganic Chemistry Monograph 2. Lappert, M. F., Ed.; American Elsevier: New York, 1973; Chapter 7, and references cited therein. (a) Murphy, M. K.; Beauchamp. J. L. J. Am. Chem. SOC. 1976, 98,5781. (b) Murphy, M. K.; Beauchamp. J. L. lbid. 1977, 99, 2085. Apeloig, Y.; Schleyer, P. V. R. Tetrahedron Lett. 1977, 4646. Numerous lines of evidence support this postulation, e.g., calculations on HZN-stabilized silicenium ions4and the structure of amino-substituted dicoordinate phosphorus cations [Cowley, A. H.; Cushner, M. C.; Szobota, J. S. J. Am. Chem. SOC.1978, 100, 77841. (a) Fleming, S.;Lupton, M. K.; Jekot, K. lnorg. Chem. 1972, 11. 2534. (b) Thomas, M. G.; Schultz, C. W.; Parry, R. W. /bid. 1977, 16, 994. The authors are indebted to Dr. Thomas A. Albright of the University of Houston for the 29SiNMR data. Wannagat. U.; Burger, H.; Hofler, F. Monatsh. Chem. 1968, 99, 1198. Riley, P. E.; Davis, R. E. Acta Crystallogr., Sect. 6 1976, 32, 381. Program package MULTAN: Main, P.; Woolfson, M. M.; Declercq, J. P.; Germain, G. 1974. A listing of principal computer programs used in this work is given in ref 9. "International Tables for X-ray Crystallography", Vol. IV; Kynoch Press: Birmingham, England, 1974. Zachariasen, W. H. Acta Crystallogr., Sect. A 1968, 24, 212. See paragraph at end of paper regarding supplementary material. Vilkov. L. V.; Tarasenko, N. A. Chem. Commun. 1969, 1176. Cowley, A. H.; Davis, R. E.; Lattman, M.; McKee, M.; Remadna, K. J. Am. Chem. SOC.1979, 101,5090. (17) Cowley, A. H.; Riley, P. E.; Szobota, J. S.; Walker, M.L. J. Am. Chem. SOC., 1979, 101, 5620. (18) Pauling, L. "The Nature of the Chemical Bond", 3rd ed.; Cornell University Press: Ithaca. N.Y.. 1960; p 246. (19) Kwart, H.; King, K. G. "d-Orbitals in the Chemistry of Silicon, Phosphorus and Sulfur", Reactivity and Structure Concepts in Organic Chemistry, Vol. 3; Springer-Verlag: New York, 1977. (20) See, for example, Cowley, A. H.; Mitchell, D. J.; Whangbo, M.-H.; Wolfe, S. J. Am. Chem. SOC.1979, 101, 5224. (21) Almenningen, A.; Haaland, A.; Haugen, T.; Novak. D. P. Acta Cbem. Scad. 1973, 27, 1821. (22) Vriezen, W. H. N.; Jellinek, F. Chem. Phys. Lett. 1967, 1, 284.
Synthesis and Crystal Structure of Bis(triphenylantimony catecholate) Hydrate. A New Square-Pyramidal Antimony( V ) Compound Michael Hall and D. Bryan Sowerby* Contributionf r o m the Department of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, England. Received July 12, 1979
Abstract: Reaction between triphenylantimony dichloride and catechol in the presence of ammonia yields the partially hydrated product ( P ~ ~ S ~ O ~ C ~ H & -the H Zcrystal O . structure of which has been determined by single-crystal X-ray diffraction methods. The compound, bis(2,2,2-triphenyl- 1,3,2-benzodioxastibole) hydrate, crystallized in the monoclinic space group P21/c with cell constants a = 9.78 (1) A, b = 21.10 ( I ) A, c = 19.95 ( I ) A, p = 105.28 (S)', Z = 4.Antimony atoms in both five- and sixfold coordination are present with the central atom in the former being attached to three carbon and two oxygen atoms in a distorted square-pyramidal arrangement. Distortion of this polyhedron arises basically from the presence of the dioxo chelating group. The second polyhedron is distorted octahedral and is derived from the square-pyramidal arrangement above with the addition of a water molecule weakly coordinated in the sixth position.
Trigonal bipyramidal or square pyramidal based structures are generally considered possible for compounds in which the central atom has ten electrons in its valence shell. The difference in energy between these two forms is apparently small but, while both arrangements are found when the central atom is a transition element, compounds derived from maingroup elements have with very few exceptions the trigonal0002-7863/80/ I502-0628$01 .OO/O
bipyramidal configuration. The major exception is the square-pyramidal structure found for pentaphenylantimony' where crystal-packing effects are thought to stabilize this geometry a t the expense of the "expected" trigonal-bipyramidal form.* It is worth stressing the unusual situation with SbPhs, as the p-tolyl antimony derivative3 and pentaphenyl derivatives of arsenic and phosphorus5 all have trigonal-bipyramidal 0 1980 American Chemical Society
